DESCRIPTION: (Applicant's Abstract) Previous studies by the applicant indicated that BCR/ABL, a leukemogenic tyrosine kinase, activates phosphatidylinositol-3 kinase (PI-3K), which plays an essential role in BCR/ABL-induced leukemogenesis. The objective of the proposed research is to examine molecular interactions between BCR/ABL and PI-3K, to determine the crucial downstream effectors of PI-3K, and to investigate if simultaneous inhibition of BCR/ABL and PI-3K has synergistic anti-leukemia effect. The first aim of this application is focused on examination of the mechanisms of BCR/ABL-PI-3K interactions. For this purpose various PI-3K mutants will be tested. Also, the intermediating proteins will be identified and their role in BCP/ABL-PI-3K interaction will be determined. The second aim is to investigate the mechanisms of activation of the downstream effectors of PI-3K in BCR/ABL-mediated transformation. The already known effectors such as Akt and Raf-1 will be assayed. The third aim is to examine the role of PI-3K and its downstream effectors in the malignant progression of CML from chronic phase to blast crisis. For this reason, a murine model will be employed consisting of the BCR/ABL-induced transformation of p53+/+ and P53-/- bone marrow cells. The fourth aim is to determine if simultaneous inhibition of BCR/ABL and PI-3K exerts synergistic antileukemia effect. Previous studies by the applicant revealed that downregulation of BCR/ABL expression by an antisense strategy or inhibition of PI-3K by its specific inhibitor wortmannin (WT), strongly inhibited proliferation of chronic myelogenous leukemia cells without affecting normal hematopoiesis. Preliminary data indicate that simultaneous inhibition of both BCR/ABL and PI-3K exerts synergistic antileukemia effect. The BCR/ABL antisense strategy and the ABL specific inhibitor will be employed to down modulate BCR/ABL, and PI-3K activity will be simultaneously inhibited by WT. Bone marrow purging experiments will be performed to test the antitumor effectiveness of the simultaneous inhibition of BCR/ABL and PI-3K in conditions mimicking those of bone marrow purging. Finally, the applicant will test the effects of a systemic therapy consisting of simultaneous inhibition of BCR/ABL and PI-3K using the applicant's in vivo models of CML in SCID mice.